1Left; the left-hand side. The fundamental directional/positional word paired with 右 ("right") — used in giving directions (左に曲がる "turn left"), describing layout (左側 "left side," 左から〜番目 "~th from the left"), and referring to sides of the body (左の足 "left leg").
次の信号を左に曲がってください。
Please turn left at the next traffic light.
駅の出口は左にあります。
The station exit is on the left.
写真の左から二番目が私の妹です。
The second person from the left in the photo is my younger sister.
イギリスでは車は道路の左を走る。
In the UK, cars drive on the left side of the road.
本棚の左の方に辞書が並んでいる。
The dictionaries are lined up on the left side of the bookshelf.
2The left hand itself. Used in expressions like 左で書く ("write with one's left") or 左に持つ ("hold in the left") to specify which hand performs an action. Essentially equivalent to 左手 (ひだりて).
彼は左で字を書く、いわゆる左利きだ。
He writes with his left hand — what's called a left-hander.
右が痛いので、しばらく左で箸を使っている。
My right hand hurts, so I've been using my left for chopsticks for a while.
ピアノは右と左で違う動きをするので難しい。
Piano is hard because the right and left hands move differently.
3The political left; the left wing. Refers to socialist or progressive ideologies and forces. Appears in phrases like 左に偏る ("lean to the left") and 左寄り ("left-leaning"), though 左翼 (さよく) and 左派 (さは) are more explicit terms.
あの新聞は明らかに左寄りの論調だ。
That newspaper has a clearly left-leaning editorial stance.
学生時代、彼は左の運動に熱心に参加していた。
In his student days, he was actively involved in left-wing activism.
4An archaic colloquial term for someone fond of drinking — a drinker. Said to derive from 左党 (sato / hidaritō, literally "left-party," a slang term for drinkers), but standalone 左 with this meaning is virtually never used in modern speech and now appears only in dictionaries and older writing.